1. Field of the Invention
The present invention relates to a GaN based semiconductor element such as a GaN based field effect transistor.
2. Description of the Related Art
Since GaN based semiconductor elements have large band-gap energy and are superior in a high temperature operation due to a high degree of heat resistance, developments of field effect transistors (FET) that use those materials, in particular, GaN/AlGaN based semiconductor, are undergoing.
As conventional GaN based field effect transistors, for example, a technique disclosed in Patent Document is known in the art. The GaN based field effect transistor is comprised of: a source electrode and a drain electrode; a channel region comprising a first GaN based semiconductor material which is i-GaN based semiconductor material or p-GaN based semiconductor material, formed to electrically connect the source electrode and the drain electrode; a first electrode supply region and a second electrode supply region spaced apart from each other, comprising a second GaN based semiconductor material which has larger band-gap energy than the first GaN based semiconductor material, and jointed with the channel region; an insulating layer formed on a surface of the channel region which locates between the first and second electrode supply region; and a gate electrode formed on the insulating layer. According to the conventional technique, a GaN based field effect transistor is obtained with normally-off type, which has low on-resistance and is capable of operating with large electronic current.
Patent Reference: No. WO 03/071607
In the conventional normally-off type GaN based field effect transistor described above, it is difficult to control a threshold, and the threshold ranges from 0 V to +1 V.